Filtering apparatus, back wash method therefor, filtering device and power plant

ABSTRACT

A filtering apparatus having a vessel and a filter made from fluororesin and treated before filtering operation by at least one of adding thermal treatment in gas or liquid and penetrating with fluid composed of hot water or steam at a temperature of less than melting point of the fluororesin.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of application Ser. No.11/183,173, filed Jul. 18, 2005, which is a continuation of U.S.application Ser. No. 10/059,326, filed Jan. 31, 2002, the entirecontents of which is incorporated herein by reference.

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2001-24855 filed on Jan. 31,2001, and No. 2001-79375 filed on Mar. 19, 2001, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a filtering apparatus and a filtering devicefor removing suspended solid contained in hot water and a power plant inwhich the filtering apparatus or the filtering device is installed.

2. Description of the Related Art

Conventionally, in a case of removing suspended solid generated fromstructural material or piping material by a condenser in a power plant,especially removing iron oxide, hollow fiber filter apparatus made frompolyethylene is used before heating feedwater. Moreover, for removingsuspended solid in hot water after heating feedwater, a metallic filteror an electromagnetic filter, etc., is used. For example, it is shown inJapanese Patent Disclosure (Koukai) No. H10-339793.

However, by using a filtering apparatus with the filter mentioned above,although a filter or a filtration material which has the mechanism toreduce concentration of the suspended solid is installed for suppressingprevention of heat transmission and corrosion inside of piping, sinceheat-resistant temperature of the above-mentioned hollow fiber filterapparatus made from polyethylene is about 60 degrees Centigrade, itcannot be applied to a feedwater heater. In addition, the suspendedsolid which exists in feedwater is also generated in the feedwaterheater.

Moreover, a metal filter has subjects that it is chemically unstable,and a used metallic material may begin to dissolve and corrode or forman oxide film, and thus pores of the filter may be blocked. Furthermore,an electromagnetic filter has deferrization performance that is greatlyinfluenced by quality of the suspended solid.

In regard to a general heat-resistant filter module composed of a hollowporosity film, a manufacturing method composed of pouring resins of lowviscosity, such as an epoxy resin, a urethane resin, and a siliconeresin, into the gap of an outer case and the hollow porosity film andheating the resin to harden is learned. For example, it is shown inJapanese Patent Publication (Koukoku) No. S44-5526, and Japanese PatentPublication (Koukoku) No. S56-40602.

However, even if the hollow porosity film itself is a material havingsufficient performance from a viewpoint of heat-resistance and elution,the amount of elution from these resins used as an encapsulant is largeand inadequate, and it is difficult to apply these resins to a filterfor removing suspended solid from hot water in the temperature of over100 degrees Centigrade, such as feedwater or heater drain of a powerplant whose water quality is highly managed.

In order to solve this problem, it is proposed a method of manufacturinga filter module, with heat-resistance and little elution, made from onlyfluororesin as the hollow porosity film and to seal the hollow porosityfilter with a thermoplastic fluororesin. For example, it is shown inJapanese Patent Publication (Touroku) No. 2993217.

FIG. 21 is a sectional view showing an example of a seal portion of afilter module of the hollow porosity film obtained by theabove-mentioned conventional method.

As shown in FIG. 21, in a filter module 104 of the hollow porosity film,a hollow porosity film 102 made from polytetrafluoroethylene (PTFE),which is a kind of fluororesin, is settled inside of an outer case 101and sealed with polytetrafluoroethylene-hexafluoropropylene copolymer(FEP) to form a support portion 103 of FEP. The outer case 101 can bemade from metals, such as stainless steel, PTFE, FEP,etrafluoroethylene-perfluoroalkylvinylether copolymer (PFA), etc. FEPand PFA of fluororesins are suitable for a thermoplastic resin which canbe used as an encapsulant.

By this method, since a filter module can be composed of metal andfluororesin only, or fluororesin only, from a viewpoint of necessarycondition of heat-resistance and elution required as a filter fordissociating suspended solid contained in the hot water of a powerplant, this filter is improved rather than a conventional filter havingthe above-mentioned problem.

By the way, in order to prevent lowering of heat-conductivity byextraction and precipitation of suspended solid or a dissolutioncomponent contained in water to piping, or to prevent vibration of apump, in the above-mentioned conventional power plant, a filteringapparatus or a desalination equipment is installed to remove suspendedsolid and ions in the water.

By installing a filtering apparatus composed of the above-mentionedfilter made from polyethylene, suspended solid in condensate at lowtemperature can be removed, however, the filter made from polyethyleneis not applicable for removing suspended solid generated in hot water ata temperature of not less than 100 degrees Centigrade becauseheat-resistant temperature of the polyethylene filter is low.

Moreover, the metallic filter applied to feedwater at a temperature ofover 100 degrees Centigrade tends to be chemically unstable and cloggedup with deposit of solid substances, and it may pollute water by elutionfrom the filter material in view of standard water quality control,therefore applying the metallic filter to hot water is difficult.

On the other hand, the electromagnetic filter has low filteringperformance because it can remove only magnetized suspended solid, andit is difficult for the electromagnetic filter to reproduce the filterfor removing dissociated suspended solid.

Furthermore, the filter shown in FIG. 21 cannot avoid heat cycles fortreating hot water of a power plant, and the filter module 104 tends tobe damaged due to expansion and contraction and exfoliation of the outercase 101 and the support portion 103, because of differences of theirmaterials and their thermal expansion coefficients.

Moreover, in a filter applied as an object for condensate filtering,back wash operation to reproduce hollow fibers which constitute thefilter is performed. In this case, by using a fact that gas cannot passthrough the film at a pressure which is lower than a bubble point, whichis the minimum pressure at which the gas can pass through the film, amethod of removing suspended solid deposited on a surface of the film bypressing at certain pressure which is lower than the bubble point topush out water in the upper space of the filtering apparatus is adopted.

On the other hand, a hydrophobic filter applied to such as a power plantmust be made hydrophilic by using alcohol, etc. before use. Although theabove-mentioned conventional method of back wash can be applied if thebubble point is more than the pressure at the back wash process, ifpacked material or a film constituting the filter has low bubble point,passing through gas in back wash makes it hydrophobic and thus it needsto be made hydrophilic. Moreover, purification process of the systemtakes additional time and medical fluid processing is also necessary.

Moreover, the back wash process of the filter used at high temperaturecannot be carried out at the high temperature, so it needs coolingprocess before the back wash process and heating process beforerestarting. Therefore, it needs to be furnished for cooling and heating,and it additionally takes long time to restart the filter because longcooling time and long heating time is included.

In the above-mentioned conventional filtering apparatus, there areseveral awaiting solution. That is, the hollow fiber filter made frompolyethylene cannot be applied to a feedwater heater because itsheat-resistant temperature is about 60 degrees Centigrade, and the metalfilter is chemically unstable and its used metallic material dissolvesand its pores may be blocked due to corrosion in proportion to formingan oxide film, and the electromagnetic filter has deferrizationperformance that is greatly influenced by quality of the suspendedsolid.

Furthermore, the filter shown in FIG. 21 cannot avoid heat cycles fortreating hot water of a power plant, and the hollow porosity film 102tends to be damaged due to expansion and contraction of the outer case101 and the support portion 103 whose thermal expansion coefficientsdiffer each other, and thus pollution of water quality is occurred dueto the base of the filter. And it is difficult to reproduce the filter,thus it is difficult to use as a filter for removing suspended solidcontained in hot water of a power plant in which highly management ofwater quality and long-term stable performance are needed.

And in the conventional back wash method of a filtering apparatus, ifthe bubble point of packed material or a film constituting the filter islow, making the filter hydrophilic is necessary because passing gases inthe back wash process makes the filter hydrophobic. And excessivepurification process of the system and medical fluid processing are alsoneeded.

Moreover, it needs cooling before the back wash process and heatingbefore restarting because it cannot back wash the filter used in hightemperature circumstance without cooling, so it needs time andadditional facilities for cooling and heating and it takes long time upto restarting.

Recently it is found that fluororesin is chemically stable under hotwater especially with the temperature of over 150 degrees Centigrade.However, since the fluororesin filter is manufactured by pulling filterbase element, if the fluororesin filter contacts with hot water infiltering operation, the fluororesin filter tends to deformed and thepermeability of the fluororesin is lowered and damaged because of heatcycle.

SUMMARY OF THE INVENTION

Accordingly, an object of this invention is to provide a filteringapparatus which is chemically stable and a back wash method for afiltering apparatus, for removing suspended solid contained in hot waterproperly without considering elution from the filter, for satisfyingwater quality control because the amount of the elution is little, andfor preventing damages of the filter and lowering of permeability of thefilter because of the heat cycle.

Another object of this invention is to provide a filtering device whichdoes not need complex system and additional process to make the filterhydrophilic in every back wash operation, for back washing at hightemperature and with convenient system structure.

Still another object of this invention is to provide a power plant forremoving the suspended solid contained in hot water such as feedwater orheater drain by applying the above-mentioned filtering apparatus orfiltering device.

Additional purposes and advantages of the invention will be apparent topersons skilled in this field from the following description, or may belearned by practice of the invention.

According to an aspect of this invention, there is provided a filteringapparatus including, a vessel adapted for connecting a feed inlet linefor introducing feed into the vessel and a filtrate outlet line forletting filtrate flow out of the vessel, a filter contained in thevessel for filtering the feed to let filtered feed flow as the filtrate,and the filter being made of fluororesin to which thermal treatment isadded beforehand by at least one of heating the filter in at least oneof gas and liquid and penetrating the filter through permeation fluidcomposed of at least one of hot water and steam.

According to an aspect of this invention, there is provided a method ofmanufacturing a filtering apparatus, including, making a filter forfiltering feed from fluororesin, adding thermal treatment to the filterby at least one of heating the filter in at least one of gas and liquidand penetrating the filter through permeation fluid composed of one ofhot water and steam, and after the adding of thermal treatment to thefilter arranging the filter in a vessel adapted for connecting a feedinlet line for introducing the feed into the vessel and a filtrateoutlet line for letting filtrated feed flow as filtrate out of thevessel.

According to another aspect of this invention, there is provided a backwash method for back washing a filtering apparatus composed of a vesseland a filter made from fluororesin to which thermal treatment is addedby using at least one of gas and liquid beforehand, the vessel beingcomposed of a first compartment in which the filter is contained tofilter feed in a filtering operation and a second compartment positionedabove the first compartment to contain filtered feed as filtrate in thefiltering operation, the back wash method including, first back washingthe filter composed of, supplying back wash rinse fluid composed of atleast one of water, air and steam into the filtering apparatus from thesecond compartment side of the filtering apparatus, passing the backwash rinse fluid through the filter, and discharging the back wash rinsefluid out of the filtering apparatus; and second back washing the filtercomposed of, supplying back wash water into the filtering apparatus fromthe first compartment side of the filtering apparatus, passing the backwash water through the filter, and discharging the back wash water outof the filtering apparatus from the second compartment side of thefiltering apparatus.

According to another aspect of this invention, there is provided afiltering device including, a filtering apparatus composed of a vesselwith a filtrate accumulation space provided in an upper side thereof anda filter contained in the vessel, a feed inlet line for introducing feedinto the filtering apparatus, a filtrate outlet line for lettingfiltrate flow out of the filtering apparatus, the filter filtering thefeed to let filtered feed flow as the filtrate, a back wash tank forstoring back wash water to be supplied into the filtering apparatus witha partition which easily passes liquid component and hardly passes gascomponent to separate the back wash tank into a first compartment and asecond compartment, the first compartment being adapted for connecting agas supply line capable of controlling gas pressure and for supplyingthe gas to the filtering apparatus, and a make-up water supply line forsupplying the back wash water to the filtering apparatus, and the secondcompartment being connected to the filtrate accumulation space of thefiltering apparatus.

According to still another aspect of this invention, there is provided afiltering device including, a filtering apparatus composed of a vesselwith a filtrate accumulation space provided in an upper side thereof anda filter contained in the vessel, a feed inlet line for introducing feedinto the filtering apparatus, a filtrate outlet line for lettingfiltrate flow out of the filtering apparatus, the filter filtering thefeed to let filtered feed flow as the filtrate, a drain line fordischarging fluid in a lower side of the filtering apparatus out of thefiltering apparatus from an inlet side of the feed, and a coolerinstalled in the drain line for cooing the discharging fluid.

According to still another aspect of this invention, there is provided apower plant including, a steam generator for generating steam fromfeedwater, a turbine driven by the steam supplied from the steamgenerator, a condenser for condensing the steam extracted from theturbine into condensate, a feedwater line for supplying the condensatefrom the condenser to the steam generator as the feedwater, a heater forheating the feedwater flowing in the feedwater line, a heater drain linefor supplying drain discharged from the heater to the feedwater line,and any of the above-mentioned filtering apparatus and theabove-mentioned filtering device installed in at least one of thefeedwater line and the heater drain line.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein:

FIG. 1 is a basic block diagram showing a filtering apparatus of a firstembodiment of this invention;

FIGS. 2A and 2B are basic block diagrams showing examples of thisembodiment while the fluororesin filter 3 is formed in hollow shapeinstalled in the tank 2, FIG. 2A shows an example that the hollowfluororesin filter is installed in the shape of character U, and FIG. 2Bshows an example that the hollow fluororesin filter is installed in theshape of character I;

FIG. 3 is a basic block diagram showing an example of this embodimentwhile the fluororesin filter installed in the tank is formed in theshape of pleats;

FIG. 4 is a basic block diagram showing a filtering apparatus of asecond embodiment of this invention;

FIG. 5 is a basic cross sectional view of a preparing equipment of afilter module of a filtering apparatus of a third embodiment of thisinvention;

FIG. 6 is a graph showing relation between the pressure difference andthe permeability concerning a filter penetrating hot water withoutthermal treatment of the filter module and a filter penetrating hotwater with heated holding for 1 hour in an atmosphere (air A) at atemperature of 200 degrees Centigrade by using the preparing equipmentshown in FIG. 5;

FIG. 7 is a basic cross sectional view of a preparing equipment of afilter module of a filtering apparatus of a fourth embodiment of thisinvention;

FIG. 8 is a graph showing change of fluorine elution velocity at thetime of the film immersion in hot water by using an autoclave;

FIG. 9 is a sectional view showing a module seal portion of a filteringapparatus of a fifth embodiment in this invention;

FIG. 10 is a sectional view showing module seal portion of a filteringapparatus of a sixth embodiment of this invention;

FIG. 11 is a schematic block diagram showing a filtering device of aseventh embodiment of this invention;

FIG. 12 is a schematic block diagram showing a filtering device of aneighth embodiment of this invention;

FIG. 13 is a schematic block diagram showing a filtering device of aninth embodiment of this invention;

FIG. 14 is a basic block diagram showing a power plant of a tenthembodiment of this invention;

FIG. 15 is a basic block diagram showing a power plant of a eleventhembodiment of this invention;

FIG. 16 is a basic block diagram showing a power plant of a twelfthembodiment of this invention;

FIG. 17 is a basic block diagram showing a power plant of a thirteenthembodiment of this invention;

FIG. 18 is a basic block diagram showing a power plant, which is aexample of installing a filtering apparatus of any of theabove-mentioned first through ninth embodiment in a boiling waterreactor (BWR) power plant;

FIG. 19 is a basic block diagram showing a power plant, which is aexample of installing a filtering apparatus of any of theabove-mentioned first through ninth embodiment in a pressurized waterreactor (PWR) power plant;

FIG. 20 is a basic block diagram showing a power plant, which is aexample of installing a filtering apparatus of any of theabove-mentioned first through ninth embodiment in a thermal power plant;and

FIG. 21 is a sectional view showing an example of a seal portion of afilter module of the hollow porosity film obtained by a conventionalmethod.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, theembodiments of this invention will be described below.

First Embodiment

FIG. 1 is a basic block diagram showing a filtering apparatus of a firstembodiment of this invention. As shown in FIG. 1, a filtering apparatus1 has a tank 2 as a vessel having a filter 3 made of fluororesin inside,and feed inlet line 4 a into which feed flows is connected to the bottomof the tank 2, and filtrate outlet line 4 b from which filtrate isdischarged is connected to the upper part of the tank 2. Here, the feedis a solution before filtering operation by the filter 3, and thefiltrate is filtered feed by the filter 3.

The feed inlet line 4 a is, for example, a feedwater line which connectsa condenser of a power plant to a reactor pressure vessel or a steamgenerator (not illustrated), which contains suspended solids, such asiron, during water feeding.

Moreover, the fluororesin filter 3 made of a polytetrafluoroethylene(PTFE) resin is formed in hollow shape or the shape of pleats, and aplurality of pores whose diameter are in the range between 0.01micrometer and 5 micrometer are made on the surface of the filter 3. Inaddition, more preferable range of the diameter is between 0.05micrometer and 0.45 micrometer.

Furthermore, the fluororesin filter 3 is a filter to which thermaltreatment for 1 hour or more in hot water or gas at a temperature ofexceeding or near the service temperature of the fluororesin filter 3 isadded beforehand.

FIGS. 2A and 2B are basic block diagrams showing examples of thisembodiment while the fluororesin filter 3 is formed in hollow shapeinstalled in the tank 2. FIG. 2A shows an example that the hollowfluororesin filter is installed in the shape of character U, and FIG. 2Bshows an example that the hollow fluororesin filter is installed in theshape of character I.

In FIG. 2A, the hollow fluororesin filter 3 a is installed in the shapeof character U by the both ends of the hollow fluororesin filter 3 abeing held by a seal portion 5.

And in FIG. 2B, the hollow fluororesin filter 3 a is installed in theshape of character I by the end of the hollow fluororesin filter 3 abeing held by a seal portion 5.

The seal portion 5 holding the hollow fluororesin filter 3 a is arrangedat the upper part in the tank 2, it has a function as a diaphragm of thefeed and the filtrate. The material of the seal portion 5 is chosen frommaterials which have durability in high temperature water, for example,stainless steel or tetrafluoroethylene-hexafluoropropylene copolymerresin (FEP), or tetrafluoroethylene-perfluoroalkylvinylether copolymerresin (PFA).

FIG. 3 is a basic block diagram showing an example of this embodimentwhile the fluororesin filter installed in the tank 2 is formed in theshape of pleats. As shown in FIG. 3, the pleats-type fluororesin filter3 b is fixed by one end of the filter 3 b being held by a seal portion5, and another end of the filter 3 b being fixed by a pleats-type filterfixing plate 7 supported by a pleats-type filter support plate 6.

Next, a function of this embodiment is explained. For example, feeddischarged from a condenser of a power plant flows in the tank 2 throughthe feed inlet line 4 a, and in this tank 2, the feed is filtrated withthe fluororesin filter 3, which is similar for the hollow fluororesinfilter 3 a or the pleats-type fluororesin filter 3 b.

Here, since many pores of the diameter between 0.01 micrometers and 5micrometers are arranged on the fluororesin filter 3, a suspended solidcomponent whose diameter is more than the diameter of the pore iscollected on the surface of the fluororesin filter 3. Thus, the filtrateis supplied to a feedwater line (not illustrated) through the filtrateoutlet line 4 b from the upper part of the tank 2.

Thus, according to the filtering apparatus 1 of this embodiment, byarranging the filter 3 made of fluororesin which filtrates the feed inthe tank 2, it is durable under hot water, and suspended solid containedin the hot water, especially at a temperature of exceeding 150 degreesCentigrade, can be removed certainly.

For example, if the fluororesin filter is added thermal treatment bysoaking the filter in hot water at a temperature of 200 degreesCentigrade before filtering operation, the concentration of fluorinewhich elutes from the fluororesin is not exceeding 100 ppt, which is notin the extent causing corrosion of piping components, thus the waterquality of the filtrate can be kept adequate, and the suspended solidcan be reduced.

Moreover, by using a heat-treated filter which is heated in hot water orgas at a temperature of exceeding or near the service temperature for 1hour or more as the fluororesin filter 3, it can reduce impurities whichelute from the filter material and keep adequate water quality of thefiltrate.

In addition, though in this embodiment tetrafluoroethylene resin is usedas a material of the fluororesin filter 3, fluororesins other than thiscan be applied.

Second Embodiment

FIG. 4 is a basic block diagram showing a filtering apparatus of asecond embodiment of this invention. In this embodiment, while using thereference number same used in the above-mentioned first embodiment to anidentical or corresponding portion of the first embodiment, onlydifferent composition and different effect from the above-mentionedfirst embodiment are explained. And in this embodiment, inside structureof a tank 2 in this embodiment is the same as the above-mentioned firstembodiment.

In this embodiment, in order to remove suspended solid adhering tosurface of the fluororesin filter 3, back wash equipment which enablesback wash operation by using back wash rinse fluid composed of at leastone of water, air, and steam, is installed.

That is, as shown in FIG. 4, one end of a back wash line 8 for sendingback wash rinse fluid into the tank 2 is connected to the upper part ofthe tank 2, and the other end of the back wash line 8 is connected to aback wash equipment 9. A back wash line 8 a connects the lower part ofthe tank 2 to the back wash equipment 9. And a fluid discharge line 10for discharging the back wash rinse fluid, etc., out of the tank 2 isconnected to one compartment under filtrate accumulation space that isin the upper part of the tank 2.

Moreover, at the lower part of the tank 2, one end of a scrubbing airsupply line 11 for supplying scrubbing air to the tank 2 is prolonged tothe inside of the tank 2, and a scrubbing air supply equipment 12 isconnected to the another end of the scrubbing air supply line 11.

And a fluid discharge line 13 for discharging fluid in the filtrateaccumulation space of the tank 2 is connected to the upper part of thetank 2, and a drain line 14 for discharging suspended solid thatprecipitates at the bottom of the tank 2 is connected to the bottom ofthe tank 2.

Next, a function of this embodiment is explained. Suspended solidcontained in feed adheres to the surface of the fluororesin filter 3. Ifthe filtering process is continued without removing the suspended solid,since pressure loss inside of the tank becomes large, the pressurebalance between at the entrance part of the tank 2 and at the exit partof the tank 2 becomes large, which blocks flow of the feed, therefore,the amount of filtration per unit period and filtering efficiency becometo lower. Moreover, a part of suspended solid is pushed away and becomesa factor to worsen the water quality at the exit part of the tank 2.

Then, in order to keep the flow rate and water quality of the filtrateadequate, it is necessary to stop pouring the feed through the filteringapparatus 1 at the time the pressure balance is reached to apredetermined level, and afterward to remove the suspended solid adheredto the surface of the fluororesin filter 3 by using the back wash rinsefluid such as water, air, and steam.

The filtering apparatus 1 is separated into a first compartment tocontain feed to be filtered by the filter 3 in the filtering operationand a second compartment, which is above the first compartment, tocontain filtrate in the filtering operation. In this embodiment, twoback wash operations described below are carried out toward thefiltering apparatus 1 with the above-mentioned composition by stoppingthe filtering operation.

That is, after stopping pouring the feed from the feed inlet line 4 a tothe tank 2 by closing a valve (not illustrated) installed in the feedinlet line 4 a, as a first back wash operation, back wash rinse fluidcomposed of at least one of water, air, and steam is supplied into thesecond compartment side of the tank 2 from the back wash equipment 9through the back wash line 8, thus the supplied rinse fluid runs throughthe fluororesin filter 3 in the first compartment side and is dischargedthrough the fluid discharge line 10 with accompanying the suspendedsolid which adhered to the surface of the fluororesin filter 3. By thisfirst back wash operation, the suspended solid, which adhered to thesurface of the fluororesin filter 3, is removed.

Moreover, as a second back wash operation, back wash water is suppliedinto the first compartment side of the tank 2 through the back wash line8 a from the back wash equipment 9, and passed through the fluororesinfilter 3, and the supplied water is discharged through the fluiddischarge line 13 or the filtrate outlet line 4 b of the firstcompartment side of the tank 2. At this moment, the inflow amount isarranged so that generated pressure difference between the firstcompartment side and the second compartment side in the tank 2 is morethan bubble point of the fluororesin filter 3. The bubble point is anecessary pressure difference between the first compartment and thesecond compartment for ventilating air through a film of the filter 3when the film is damped with alcohol. By adjusting the flow of the backwash water so that the pressure difference is not less than the bubblepoint of the filter 3 by relatively increasing the pressure of theupstream water, that is, the pressure of the first compartment, it makeseasier to flow the water from the first compartment side to the secondcompartment side, and the second back wash operation is properly carriedout.

Moreover, by experiments for the fluororesin filter 3 whose bubble pointis 0.1 MPa, it is confirmed that by setting the pressure differencebetween the first compartment and the second compartment to not lessthan 0.2 MPa, the proper second back wash operation can be carried outremarkably. Thus it is more preferable that the pressure difference ismore than twice as large as the bubble point.

This second back wash operation can recover the permeability that tendsto lower. Moreover, soundness of the fluororesin filter can beconfirmed.

It is preferable that the second back wash operation is carried outafter the first back wash operation, and it is more preferable that ascrubbing operation, which is explained below, is additionally carriedout after the first back wash operation and before the second back washoperation.

That is, as the scrubbing operation, scrubbing air is supplied into thetank 2 through the scrubbing air supply line 11 from the scrubbing airsupply equipment 12 and discharged through the fluid discharge line 10,therefore the fluororesin filter 3 fluctuates and then suspended solidadhered to the surface of the fluororesin filter 3 is removed by theshaking of the filter. And the suspended solid removed from the surfaceof the fluororesin filter 3 and precipitated at the bottom of the tank 2is discharged through the drain line 14.

In addition, in this embodiment, both hollow-like fluororesin filter 3 aand pleats-type fluororesin filter 3 b are applicable. Moreover, it isalso applicable to install chemical wash equipment for cleaning thefilter with chemicals instead of the back wash equipment 9 in thisembodiment. The chemicals used in this chemical wash equipment are, forexample, hydrogen peroxide, or acid such as hydrochloric acid, sulfuricacid, nitric acid, and oxalic acid, or alkali such as sodium hydroxide.

Thus, according to this embodiment, by back wash the fluororesin filter3 by the back wash equipment 9, or by cleaning the fluororesin filter 3by the chemical cleaning equipment, stains caused by the suspended solidwhich adhered the surface of the fluororesin filter 3 can be removed.Moreover, the suspended solid which loosely adhered to the surface ofthe fluororesin filter 3 can be removed by the back wash equipment 9which uses the back wash rinse fluid or the chemical wash equipment orthe scrubbing air supply equipment 12. Thus, the fluororesin filter 3can be reused without exchange, and water quality of the filtrate can bekept adequate.

Third Embodiment

FIG. 5 is a basic cross sectional view of a preparing equipment of afilter module of a filtering apparatus of a third embodiment of thisinvention.

As shown in FIG. 5, a heater 16 is buried or installed in the verticaldirection in a sealed hollow heat treatment vessel 15, and inside of theheat treatment vessel 15 is filled with air A. A filter module 7 madefrom PTFE, which is a kind of a fluororesin, is contained in the heattreatment vessel 15, and the filter module 7 is heated as the internalair A is heated by the heater 6.

FIG. 6 is a graph showing relation between the pressure difference andthe permeability concerning a filter penetrating hot water withoutthermal treatment of the filter module and a filter penetrating hotwater with heated holding for 1 hour in an atmosphere (air A) at atemperature of 200 degrees Centigrade by using the preparing equipmentshown in FIG. 5.

As shown in FIG. 6, the filter module 17 from which the residual stressis removed by thermal treatment in air beforehand for suppressing heatmodification at the time of hot water permeation has no change in thepermeability even if the hot water permeation is carried out repeatedly,so fluorine which elutes from PTFE is reduced. As shown in Example 1 ofTable 1, the value 100 designates a reference point of the permeabilityand the amount of elution of the fluororesin in this case.

Moreover, the following Table 1 shows about a filter module which isheld and prepared in inert gas at 100 degrees Centigrade for 2 hours asan Example 2, a filter module which is held and prepared in inert gas at250 degrees Centigrade for 1 hour as an Example 3, a filter module whichis held and prepared in pure water at 150 degrees Centigrade for 1 houras an Example 4, a filter module which is held and prepared in purewater at 200 degrees Centigrade for 1.5 hours as an Example 5, and afilter module which is held and prepared in pure water at 250 degreesCentigrade for 1 hour as an Example 6.

On the other hand, the following Table 1 also shows a filter modulewhich is held and prepared in inert gas at 90 degrees Centigrade for 2hours as a Comparison Example 1, a filter module which is held andprepared in inert gas at 100 degrees Centigrade for 8 hours as aComparison Example 2, and a filter module which is held and prepared inpure water at 250 degrees Centigrade for 0.9 hour as a ComparisonExample 3.

In addition, in the following Table 1, it is preferable that the ratioof the permeability is not less than 100, which is a reference point,and it is allowable that the ratio of the amount of elution are no morethan 130.

TABLE 1 HEAT TREATMENT CONDITION FILTER TEMPERATURE ELUTION NUMBER(CENTIGRADE) TIME (HOUR) ATMOSPHERE PERMEABILITY* AMOUNT* EXAMPLES 1 2001 AIR 100 100 2 100 2 INERT GAS 100 120 3 250 1 INERT GAS 180 80 4 150 1PURE WATER 150 110 5 200 1.5 PURE WATER 150 90 6 250 1 PURE WATER 170 80COMPARISON 1 90 2 INERT GAS 40 130 EXAMPLES 2 100 0.8 INERT GAS 65 140 3250 0.9 PURE WATER 180 135 *100 AS A REFERENCE POINT

Clearly recognized from FIG. 6 and Table 1, as shown in Examples 1through 6, if the filter is heated for 1 hour or more in air atmosphereor pure water at a temperature of between 100 and 250 degreesCentigrade, which is below the melting point of PTFE (327 degreesCentigrade) for removing residual stress and suppressing the heatmodification before use of the filter, the permeability of the filter isimproved and the amount of elution of the fluororesin is reduced.

On the other hand, as shown in Table 1, if the temperature of the heattreatment is set under 100 degrees Centigrade, the quantity of fluorinewhich elutes from the fluororesin increases, and the permeability ismarkedly lowered as shown in Comparison Example 1. And if thetemperature of the heat treatment is 100 degrees Centigrade and theretention time is less than 1 hour, the quantity of fluorine whichelutes from the fluororesin increases, and the permeability is markedlylowered as shown in Comparison Example 2. Moreover, if the temperatureof the heat treatment is 250 degrees Centigrade and the retention timeis less than 1 hour, though the permeability improves, the quantity offluorine which elutes from the fluororesin increases as shown inComparison Example 3.

Therefore, as shown in FIG. 6, by using the filter module which has notheated, the film of the filter is deformed by the residual stress at thetime of manufacture and the permeability is lowered, at every hot waterpermeation.

By the filter module 17 obtained according to the Examples 1 through 6,the filter module 17 has stable heat-resistant cycle performance inapplying to a filtering apparatus which has frequent heat cycles of suchas heater drain and feedwater, by thermal treatment beforehand to removethe residual stress at the time of manufacture.

In addition, it takes 1 hour or more to raise the temperature in theheat treatment vessel 15 to set the temperature at the above-mentionedprocessing temperature, and after holding at the constant temperaturefor 1 hour or more and removing the residual stress, it is graduallycooled for from 3 to 6 hours. Incidentally, since rapid raise of thetemperature may damage the filter module due to the difference ofthermal expansion coefficients between different fluororesins, theraising time of the temperature is set to be not less than 1 hour, andthe longer the raising time is, the more desirable it is.

Moreover, to obtain the filter module 7 which is hard to be modified byheat at the time of use, since the longer the above-mentioned coolingtime is, the more the residual stress is, it is desirable to coolgradually as much as possible.

Furthermore, range of between 100 and 250 degrees Centigrade is suitablefor the retention temperature, and it is preferable to set thetemperature from 0 to 10 degrees higher than the temperature at the timeof manufacture of the filter module 7 or the film. Moreover, it iseffective in heating in the surroundings where the filter is used byadding thermal treatment in a solution additionally after the thermaltreatment in a gas, from a viewpoint of improving the heat-resistant ofthe filter module 17.

The above-mentioned filter module 7 is a product made from a fluororesinhaving heat-resistance and chemical resistance, and it is formed in theshape of hollow or a flat film or a tube, or in a packed column composedof a cylindrical vessel filled with pieces of granular fusuoresin aspacked material, and it is preferable that the fixing substance to afilm module is also made from a fluororesin.

Moreover, as for the gas which fills in the heat treatment vessel 15,what is not degraded the quality of the module 1 in the thermaltreatment, such as inert gas, for example, nitrogen or argon, or steam,instead of the above-mentioned air A, is desirable.

And a liquid is also possible for what is filled in the heat treatmentvessel 15 instead of gases, such as an atmosphere (air A), a kind ofliquid which does not include an impurity as a contamination of themodules, such as pure water and ultrapure water, is suitable, and it ismore desirable that the liquid has the property about pH value ordissolved oxygen concentration or chemical ingredient which is the sameof that in the use environment of the filter. Thus, according to theExamples 1 through 6 in this embodiment, since the residual stress atthe time of manufacture can be removed by adding thermal treatmentbefore the use of the module, it becomes possible to obtain a stabilizedtreatment performance against repetitive heat

Moreover, if the form of the filter module 7 made from a fluororesin isselected from the group of a hollow module, a module in the shape ofpleats, a flat film, and a tube module, the fluororesin filter havingstable permeability and less influence of pollution of water quality canbe obtained.

Fourth Embodiment

FIG. 7 is a basic cross sectional view of a preparing equipment of afilter module of a filtering apparatus of a fourth embodiment of thisinvention. It explains using the same code to a corresponding portionidentically to the above-mentioned third embodiment.

As shown in FIG. 7, hot water W fills and a filter module 17 isinstalled in the pressure vessel 18 for hot water washing. And a cooler19, a filter 20 and a desalination equipment 21 filled up with ionexchangers are installed on a line L1 whose one end is connected to theexit side of the hot water washing pressure vessel 18, and the anotherend of the line L1 is connected to a water supply side of a pump 22. Oneend of a line L2 is connected to the discharge side of the pump 22, anda heater 23 is installed on this line L2, and the another end of theline L2 is connected to the hot water washing pressure vessel 18.

Therefore, by driving the pump 12, hot washing water in the hot waterwashing pressure vessel 18 is cooled by the cooler 19, and afterwardsuspended solid is removed from the elution of the filter module 17contained in the washing water at the filter 20, and the hot water fromwhich ion ingredients are removed by the desalination equipment 21 isprovided to the pump 22. And the washing water discharged from the pump22 is heated as the hot water W, and the hot water W is supplied to theentrance side of the hot water washing pressure vessel 18.

As a result of examining the elution component in the immersion solutionafter immersing the filter module 7 of the hollow fibers made of afluororesin into the hot water, whose pressure is not less than thepressure at which it does not boils, at a temperature of 230 degreesCentigrade for 1 hour, any components other than fluorine are notdetected, and the permeability is also improved. This is shown as a caseof an Example 9 in Table 2 shown below.

Moreover, experiments immersing in hot water at a temperature of 150degrees Centigrade and 200 degrees Centigrade for 1 hour are shown as anExample 7 and an Example 8, respectively, and experiments applying steamat temperatures of 150, 200, and 230 degrees Centigrade are shown asExamples 10, 11, and 12, respectively. As shown in Table 2, theseexamples improve permeability of the filter and particularly reduce theelution amount of fluorine.

TABLE 2 HOT WATER PEAMEATION STEAM PEAMEATION HOT WATER STEAMTEMPERATURE PEAMEATION TEMPERATIRE PEAMEATION ELUTION FILTER NUMBER(CENTIGRADE) TIME (HOUR) (CENTIGRADE) TIME (HOUR) PERMEABILITY* AMOUNT*EXAMPLES 7 150 1 — — 100 115 8 200 1 — — 150 105 9 230 1 — — 160 100 10— — 150 1 120 95 11 — — 200 1 160 90 12 — — 230 1 170 80 COMPARISON 4130 0.8 — — 55 155 EXAMPLES 5 — — 130 0.8 60 150 6 — — 260 1 60 85 7  900.8 — — 30 130 8 260 0.6 — — 50 75 9 — —  90 0.8 35 135 10 — — 260 0.655 70 *100 AS A REFERENCE POINT

FIG. 8 is a graph showing change of fluorine elution velocity at thetime of the film immersion in hot water by using an autoclave. As shownin FIG. 8, after most of the fluorine elutes for several hours, theelution is hardly confirmed. It turns out that it is possible to removethe fluorine elution by thermal treatment with hot water for severalhours.

On the other hand, as shown in Comparison Examples 4 through 10 in Table2, if the permeation of hot water W with high purity or a steam at atemperature of less than 100 degrees Centigrade, the elution amount offluorine from the fluororesin increases and the permeability is markedlylowered as shown in Comparison Examples 7 and 9. And if the temperatureof the hot water or the steam is over 250 degrees Centigrade and thepermeation time is less than 1 hour, though the permeability isadequete, the quantity of the fluorine which elutes from the fluororesinincreases as shown in Comparison Examples 6, 8 and 10. Moreover, if thetemperature of the hot water W or the steam is set between 100 and 250degrees Centigrade and the retention time is less than 1 hour, thequantity of the fluorine which elutes from the fluororesin increases andthe permeability is markedly lowered as shown in Comparison Examples 4and 5.

In Table 3, Examples 13 and 14 show cases of keeping the temperature ofthe heat treatment between 100 and 250 degrees Centigrade in inert gasfor not less than 1 hour and afterward penetrating hot water W at atemperature of between 100 and 250 degrees Centigrade for not less than1 hour to the filter with the pressure of not less than the pressure atwhich it boils, and Examples 15 and 16 show cases of keeping thetemperature of the heat treatment between 100 and 250 degrees Centigradein pure water for not less than 1 hour and afterward penetrating steamat a temperature of between 100 and 250 degrees Centigrade for not lessthan 1 hour to the filter, respectively.

TABLE 3 HOT WATER STEAM PENETRATION PENETRATION HEAT TREATMENT CONDITIONHOT WATER STEAM FILTER TEMPERATURE TIME TEMPERATURE TEMPERATIRE PERMEA-ELUTION NUMBER (CENTIGRADE) (HOUR) ATMOSPHERE (CENTIGRADE) (CENTIGRADE)BILITY* AMOUNT* EXAMPLES 13 100 2 INERT GAS 150 — 120 110 14 250 1 INERTGAS 200 — 180 80 15 150 1 PURE WATER — 150 140 115 16 200 1.5 PURE WATER— 200 170 90 *100 AS A REFERENCE POINT

Clearly recognized from Table 3, by thermal treatment the filter onabove-mentioned conditions, the residual stress at the time ofmanufacture can be removed efficiently, and by penetrating the hot waterW or the steam on above-mentioned conditions, pollutant component of thewater quality generated by fluorine elution at the time of use can beremoved in a short time.

Thus, in this embodiment, since the hot water W, which penetratesthrough the filter module 17 and from which the elution component isremoved with the filter 20 and which is desalinated by the desalinationequipment 21, can be used in a circulation by using the equipment shownin FIG. 7, so the elution component is removable to decrease itsconcentration to thoroughly low level efficiently in a short time,compared with batch processing.

Moreover, although it is difficult in batch processing to remove theelution component inside of the films, by the above-mentionedcirculatory method in this embodiment the elution component inside ofthe films can be removed effectively in a short time. And if the filtermade from a fluororesin is replaced to the above-mentioned packed columnfilled up with pieces of granular fluororesins, the elution component isalso efficiently removable.

In addition, in this embodiment, the filter module 17 is washed from theoutside towards the inside of the module 17, but it is possible to washthe filter module 17 from the inside towards the outside of the module17 by reversing the exit and the entrance of the hot water washingpressure vessel 18.

Moreover, the temperature of the hot water W used in this embodiment isbetween 100 and 250 degrees Centigrade as mentioned above, and between 1hour and 1 week is suitable as for the processing time.

Furthermore, it is preferable that the hot water W of this embodiment iseither pure water, steam, or a solution obtained by imitation of usagesurroundings of a power plant concerning at least one of pH value,dissolved oxygen concentration, and at least a part of chemicalingredients.

Moreover, by gradually increasing the permeation temperature at somesteps or in a fixed velocity with removing the elution component, thedamage of the filter module 17 due to the thermal shock can be evaded,and by thermal treatment with removing the elution component, pollutionof a system due to the elution component can be suppressed, thereforethe processing time can be shortened.

Moreover, since the filter module 17 is hydrophobic, it is moredesirable to immerse the filter module 17 in alcohol, such asisopropylalcohol, to make the module hydrophilic. And by replacing theheater 23 and the cooler 19 of this embodiment with a heat exchanger, asystem can be simplified and thermal efficiency can also be improved.

Thus, in this embodiment, the filter module 17 can be washed by hotwater W and the elution component can be removed beforehand, lowering ofwater quality can be prevented when the filter is the installed to beused in a power plant.

And if the quality of the hot water W is modified by the water qualityof a power plant concerning at least one of pH value, dissolved oxygenconcentration, and at least a part of chemical ingredients, bypenetrating the hot water W whose water quality is equal or similar tothat in a usage surroundings of the filter module 17, the elutioncomponents which elute in a solution at the time of use of the filtermodule 17 under high temperature can be effectively removed beforehandby washing or material regeneration, and the pollution due to usage ofthe filter module 17 can be suppressed lower compared with a case ofmerely using hot water.

Fifth Embodiment

FIG. 9 is a sectional view showing a module seal portion of a filteringapparatus of a fifth embodiment of this invention. As shown in FIG. 9,in this embodiment, a peripheral edge of hollow porosity films 24 madefrom polytetrafluoroethylene (PTFE), which is a kind of a fluororesin,is directly sealed by melted joining by support portion 25 made fromtetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) which is athermoplastic fluororesin whose melting point is less than that of PTFE.

Next, a function of this embodiment is explained. For a filter forfiltering hot water in a power plant, a heat cycle cannot be avoided,thus in the conventional filter shown in FIG. 21, the outer case 101 andthe support portion 103, which differ in thermal expansion coefficientsof their materials, are expanded and contracted by the heat cycle, andtherefore the conventional filter module 104 is easy to be damaged.

Then, in this embodiment, by deleting the outer case 101 which maydamage the filter module by exfoliation of the seal portion due to thelarge difference of expansion and contraction of different materialsduring the heat cycle, a region where different materials touch eachother exists only between the hollow porosity film 24 and the supportportion 25, therefore the expansion and the contraction is minimized andit becomes possible to make the damage of the filter module hard tooccur.

In addition, for example, by using a sealing method shown in JapanesePatent Publication (Touroku) No. 2993217, the hollow porosity film 24can be sealed by only using thermoplastic PFA by melting, it can achieveboth the sealing and forming the support portion 25 simultaneouslywithout using other encapsulants.

Moreover, as mentioned above, it is desirable to use PTFE as the hollowporosity film 23 made from a fluororesin used in this embodiment. And asfor the thermoplastic fluororesin used as an encapsulant which formssupport portion 25, for example, PFA, FEP, ETFE,polychlorotrifluoroethylene (PCTFE), and polyvinylidenefluoride (PVdF),etc. are considered. Among them, PFA and FEP, which are heat-resistantand have excellent chemical proof against both an acid and an alkali,are the same kind of resin as a PTFE hollow fiber with high affinity,and the most suitable as the encapsulant.

Furthermore, if the heat treatment and the hot water permeation arecarried out as mentioned in the above-mentioned third and/or fourthembodiments to the filter module which is manufactured according to thisembodiment, it can obtain stable permeability and provide a filtersuitable to apply to the hot water in a power plant with less waterpollution.

Thus, according to this embodiment, the length of contacting foreignmaterials between the periphery of the hollow porosity film 24 and theencapsulant is very slight, and dimensional change due to expansion andcontraction by the heat cycle also becomes minute, and it can formstrong module seal portion against the heat cycle.

Sixth Embodiment

FIG. 10 is a sectional view showing module seal portion of a filteringapparatus of a sixth embodiment of this invention. As shown in FIG. 10,the support portion 25 made from PFA in the fifth embodiment shown inFIG. 9 is replaced with a support portion made from PTFE in thisembodiment, and a seal portion 26 composed of PFA, which has a meltingpoint lower than that of PTFE, seals between this support portion 25 andthe hollow porosity film 24.

For example, PFA tubes are covered on a seal portion of the hollowporosity film 24 made from PTFE, and the hollow porosity film 24 isseated at the seal portion 25 b made from PTFE by inserting the PFAtubes into pores formed in support portions 25 b and melting PFA likethe above-mentioned fifth embodiment.

In addition, PTFE is desirable to use as the hollow porosity film madefrom a fluororesin in this embodiment. And as a substance of the supportportion 25 b, metals, such as stainless steel, PTFE, PFA and FEP aresuitable. And suitable thermoplastic fluororesins used as an encapsulantare PFA and FEP, which are in the same kind of resin as the hollowporosity film 24 made from PTFE and have high affinity.

Moreover, if the filter module manufactured in this embodiment is heatedand permeated with hot water according to a method mentioned in thethird embodiment and/or the fourth embodiment, it can obtain more stablepermeability and provide a filter which is suitable for hot water of apower plant with less water pollution.

Thus, in this embodiment, since the length where foreign materialscontact, such as a joint of the periphery of the hollow porosity film 24and the seal portion 26 and a joint of the support portion 25 b and theseal portion 26, is very slight, the difference of the length ofexpansion and contraction due to the heat cycle also becomes minute, andit can form the support portion equipped with strong module seal portionagainst the heat cycle.

Seventh Embodiment

FIG. 11 is a schematic block diagram showing a filtering device of aseventh embodiment of this invention. A filtering device of thisembodiment has a filtering apparatus 31 composed of a vessel 2 and afilter 30 suspended with a canister plate 30 a in the vessel 2. A feedinlet line 4 a for introducing feed and a filtrate outlet line 4 b fordischarging filtrate are connected to the filtering apparatus 31,respectively. The upper part of inside of the filtering apparatus 31over the canister plate 30 a is filtrate accumulation space 37, and aback wash line for supplying back wash water 32 is connected to thefiltrate accumulation space 37 side, and a back wash tank 34 to storethe back wash water 32 is installed on the back wash line 33.

The back wash tank 34 is divided into two compartments by a partition36, which easily passes liquid component such as the back wash water 32and hardly passes gas component such as the gas 35. A gas supply linefor supplying the gas 35 and a make-up water supply line 40 forsupplying make-up water 39 are connected to a divided compartment (afirst compartment) 36 a, on the other hand, the another dividedcompartment (a second compartment) 36 b is connected to the filtrateaccumulation space 37 by the back wash line 33. A gas tank 41 is settledon the gas supply line 38 to control pressure of the supplied gas 35.

Leak lines 42 and 43 which have the leak valves 42 a and 43 a,respectively, are connected to the filtrate accumulation space 37 andthe first compartment 36 a side of the back wash tank 34, respectively.Moreover, a waste receiving tank 44 is arranged under the filteringapparatus 31, a drain lines 45 is led to the waste receiving tank 44from the upper part of the feed side of the filtering apparatus 31 belowthe canister plate 30, and a drain line 46 is led to the waste receivingtank 44 from the bottom of the filtering apparatus 31. Each line 4 a, 4b, 33, 38, 40, 45, 46 has a valves 47 a through 47 b for opening orclosing, respectively.

Next, a function of this embodiment is explained. In usual filteringprocess of feed, only the valve 47 a of the feed inlet line 4 a and thevalve 47 b of the filtrate outlet line 4 b are open and the other valvesare all closed, and the feed is supplied to the filtering apparatus 31through the feed inlet line 4 a and filtered with the filter 30, andafterward the filtrate is discharged to outer system through thefiltrate outlet line 4 b.

On the other hand, in back wash operation, the valve 47 a of the feedinlet line 4 a and the valve 47 b of the filtrate outlet line 4 b isclosed, and at first on a process preceding the back wash operation, itopens the leak valve 42 a of the leak line 42, which is connected to thefiltrate accumulation space 37, and the valve 47 c of the back wash line33 to supply the water 32 in the back wash tank 34 to the filteringapparatus 31. Thus, if gas residually stays in the filtrate accumulationspace 37, the water 32 replaces the gas, and therefore it effectivelyprevents to make the filter

Next, as back wash operation, while the temperature inside of the filter31 is kept less than 100 degrees Centigrade the valve 47 c of the backwash line 33, which connects the back wash tank 34 and the gas tank 41,is opened, it opens the valve 47 d of the gas supply line 38 to supplygas of certain pressure from the gas tank 41 to the first compartment 36a of the back wash tank 34. Thus water in the back wash tank 34 ispoured into the filtering apparatus 31 and the water passes through thefilter 30 in the direction contrary at the time of the filteringprocess. In this case, it opens the valve 47 f of the drain line 45connected to the upper part of the feed side of the filtering apparatus31 and the waste receiving tank 44 receives drain by overflowing.

That is, as mentioned above, the inside of the back wash tank 34 isdivided into two compartments by the partition 36 which can pass thewater 32 easily but is hard to pass the gas 55 and the secondcompartment 36 b is filled with the water 32 and communicated to thefiltering apparatus 31. And the gas supply line 38, the make-up watersupply line 40 for supplying the make-up water 39 with the valve 47 e isconnected to the first compartment 36 a. Thus the necessity amount ofthe make-up water for the back wash operation is supplied and the gas 35is supplied for pressurizing the water 32.

Since gas 35 is hard to pass the partition 36, when the water 32 in thefirst compartment 36 a of the back wash tank 34 is exhausted, supply ofthe water 32 to the filtering apparatus 31 stops. At this time it closesthe valve 47 d of the gas supply line 38. Next, it opens the drain valve47 f to collect suspended solid removed from the filter 30 together withwater in the filter 31. If the filter 30 is constructed as a hollowfiber filter which carries out film vibration by rise of air bubblespoured into the water, it is effective in removing the suspended solidon the filter 30 to pour gas from the lower part of the filteringapparatus 31 for performing scrubbing operation, after the back washoperation from the back wash tank 34.

Moreover, since the leak line 43 with the leak valve 43 a is connectedto the first compartment 36 a of the back wash tank 34, by opening theleak valve 43 a it can release the air and supply the make-up water 39in a short time. Therefore, it is possible to operate back washrepeatedly and to remove the suspended solid from the filtereffectively.

In addition, if the partition 36 arranged inside of the back wash tank34 is hydrophilic, that is, for example, the partition 36 is composed ofhydrophilic film or hydrophilic packed material, it is effective inprevention of making the filter 50 hydrophobic because the gas 35 andthe water 32 are easily separated each other.

Furthermore, if the partition 36 has a flat film, or a film in the shapeof pleats, or a cylindrical film, or a hollow film, to enlarge the filmarea of the partition 36, it can decrease pressure loss of the partition36 and therefore the pressure of the supplied gas 35 can be lowered.

Moreover, if the pressure of the gas 35 for pushing out the water in theback wash tank 34 is not set constant and once it stores gas in the gastank 41 and afterward it instantly supplies the water 32 of the backwash tank 34 into the filtering apparatus 31, the back wash operationcan be performed effectively. Furthermore, if the pressure of the gas 35at the time of pushing out the water in the first compartment 36 a ofthe back wash tank 34 is set below the minimum pressure at which thepartition 36 starts to pass the gas 35, it is economical by minimizingthe volume of the gas tank 41. For example, if the pressure in the gastank 41 is set ten times as large as the above-mentioned minimumpressure, the volume of the gas tank 41 can be set one ninth of that ofthe back wash water. It is adequate that the pressure at the time ofextruding the water 32 is about between 0.1 MPa and 1 MPa from aviewpoint of the passing pressure of the gas 35 through the partition36, and the pressure of the gas tank 41 is between 1 MPa and 15 MPa.

In this embodiment, since the back wash of the filter 30 can be carriedout only by gas pressurizing, without making the filter 30 hydrophobic,it can simplify equipment and reduce time concerning process to makehydrophilic and purification process of inside of the filteringapparatus to minimize restarting time of the filtering apparatus 31, andthe chemicals waste is not produced and treatment process of thechemicals waste becomes unnecessary.

In addition, as mentioned in from the first embodiment to the fourthembodiment, a fluororesin filter, which is heated beforehand in at leastone of air and solution, or permeated with hot water or steam, is alsoapplicable to the filter 30 in this embodiment.

Eighth Embodiment

FIG. 12 is a schematic block diagram showing a filtering device of aneighth embodiment of this invention. A filtering device of thisembodiment has a filtering apparatus 31 composed of a vessel 2 and afilter 30 suspended with a canister plate 30 a in the vessel 2. A feedinlet line 4 a for introducing feed and a filtrate outlet line 4 b fordischarging filtrate are connected to the filtering apparatus 31,respectively. The upper part of inside of the filtering apparatus 31over the canister plate 30 a is filtrate accumulation space 37.

And a cooler 50 for cooling drain and the valve 47 g is arranged on thedrain line 45 introduced from the bottom of the filtering apparatus 31.In addition, back wash line 33 using water is omissible in thisembodiment.

In this embodiment, in back wash operation, while it closes the valves47 a and 47 b of a system and controls flow rate by controlling theopenings of the valve 47 g with keeping high temperature and highpressure in the filtering apparatus 31, solution in the filteringapparatus 21 is cooled by the cooler 50 and then is discharged to thewaste receiving tank 44. In accordance with lowering of the pressure inthe filtering apparatus 21, water in the filtrate accumulation space 37passes through the filter 30 with expanding; thereby back wash action isperformed. That is, this pressure lowering makes the fluid passing thefilter 30 from liquid phase to steam and rapidly increases the volume ofthe fluid compared with the liquid phase.

Therefore, the volume of the medium passing the filter 30 also increasesremarkably, and it can achieve higher effect than that of washing byusing solution. Suspended solid is carried together with steam and heldin solution extracted by the cooler 50, and afterward collected in thewaste receiving tank 44.

According this embodiment, back wash operation can be performed by usingonly high-pressure hot water in the filtering apparatus 31 with keepinginside of the filtering apparatus 31 in hot condition, without coolingthe filtering apparatus 31, therefore the re-starting time of thefiltering apparatus 31 can be shortened drastically. And waste is lessgenerated because the back wash water is not supplied from outer system.

That is, according to this embodiment, back wash operation of thefiltering apparatus can be performed by using high-pressure hot water inthe filtering apparatus 31 without carrying back wash water fromoutside. Since the hot high-pressure water in the filtering apparatus isreturned to liquid phase by the cooler 50 and drained while the water ispulling out with decompressing and expanding, any large washing tank isunnecessary.

Moreover, although the water in the filtrate accumulation space 37 ofthe upper part of the filtering apparatus 31 is a liquid since thepressure is high at first, as the pressure declines, the water boils andbecomes steam and its volume expands rapidly.

Therefore, since large quantity of the steam passes through the filterat a large flex density, back wash process can be achieved with thecompressed hot water in the filtrate accumulation space of the filteringapparatus. What passes through the filter is only steam, thus it canavoid making the filter hydrophobic.

In addition, as mentioned in from the first embodiment to the fourthembodiment, a fluororesin filter, which is heated beforehand in at leastone of air and solution, or permeated with hot water or steam, is alsoapplicable to the filter 30 in this embodiment. And it is also possiblethat additional back wash equipment explained in the seventh embodimentis arranged in this embodiment.

Ninth Embodiment

FIG. 13 is a schematic block diagram showing a filtering device of aninth embodiment of this invention. A filtering device of thisembodiment has a filtering apparatus 31 composed of a vessel 2 and afilter 30 suspended with a canister plate 30 a in the vessel 2. A feedinlet line 4 a for introducing feed and a filtrate outlet line 4 b fordischarging filtrate are connected to the filtering apparatus 31,respectively. The upper part of inside of the filtering apparatus 31over the canister plate 30 a is filtrate accumulation space 37, and asteam generator 52 is connected to the filtrate accumulation space 37side of the filtering apparatus 31 by a steam line 51 having a valve 47h. And a cooler 50 for cooling drain and a valve 47 g is arranged on thedrain line 45 introduced from the bottom of the filtering apparatus 31.

According to the above-mentioned composition, in back wash operation,after draining the solution in the filtering apparatus 31 by the methodas mentioned in the eighth embodiment, it opens the valve 47 h to supplysteam 53 from the steam generator 52 to the filtering apparatus 31through the steam line 51, and suspended solid on the filter 30 iswashed and removed by the steam 53, and afterward the steam is extractedby the cooler 50 and held in solution and collected in the wastereceiving tank 44. Thus, since steam 53 can be obtained continuously,the amount of the washing steam can be adjusted freely according to anadhesion state of the suspended solid.

Moreover, it is also possible to operate back wash with steam in thesteam generator 52 after draining water in the filtering apparatus 31through the valve 47 g as the temperature inside of the filteringapparatus 31 is set less than 100 degrees Centigrade. In this case, itcan avoid making the filter 30 hydrophobic since the back wash operationcan be achieved by the steam 53 at low pressure, and the cooler 50 canbe omitted or the volume of equipment can be minimized since the steamis extracted in the filtering apparatus 51.

According to this embodiment, it can avoid making the filter 30hydrophobic because steam is used to the back wash operation, and theback wash is performed with few amounts of wastes since the steam 53 isextracted to be changed into water with remarkably decreasing thevolume.

In addition, as mentioned in from the first embodiment to the fourthembodiment, a fluororesin filter, which is heated beforehand in at leastone of air and solution, or permeated with hot water or steam, is alsoapplicable to the filter 30 in this embodiment.

Tenth Embodiment

FIG. 14 is a basic block diagram showing a power plant of a tenthembodiment of this invention. As shown in FIG. 14, the power plant ofthis embodiment is composed of a feedwater line 60 which flows feedwaterfrom a condenser 55 to a steam generator 59 through a condensatedemineralizer system 56, a low pressure heater 57, and a high pressureheater 58. In this feedwater line 60, wet steam which drove a turbine iscooled by the condenser 55 and changed into condensate, and ionicimpurities contained in this condensate is removed by the condensatedemineralizer system and the condensate becomes feedwater, and thisfeedwater is heated by the low pressure heater 57 and the high pressureheater and thus becomes hot feedwater to be supplied to the steamgenerator 59.

Moreover, the power plant of this embodiment is equipped with a mainsteam line 63 from a steam generator 59 to a high pressure turbine 61and a low pressure turbine 62, and in this main steam line, steamgenerated in the steam generator 59 drives the high pressure turbine 61and the low pressure turbine 62.

Furthermore, the power plant of this embodiment is composed of a highpressure heater drain line 64 for supplying steam from the high pressureturbine 61 extracted by the high pressure heater 58 to the feedwaterline 60, and a low pressure heater drain line 65 for supplying steamfrom the low pressure turbine 62 extracted by the low pressure heater 57to the feedwater line 60. In this heater drain lines 64, 65, steam fromthe high pressure turbine 61 and low pressure turbine 62, respectively,is heated as feedwater and afterward extracted by the high pressureheater 58 and low pressure heater 59, respectively, and the extractedwater, that is, drain, is returned to the feedwater line 60.

And in the power plant of this embodiment, two or more filteringapparatuses 66 of any of the above-mentioned first through ninthembodiments is installed in the feedwater line 60 between the condenser55 and the steam generator 59 through the condensate demineralizersystem 56, the low pressure heater 57, and the high pressure heater 58.

That is, in the feedwater line 60, these feedwater filtering apparatuses66 are installed on the inlet side of the low pressure heater 57 and theinlet side and the outlet side of the high pressure heater 58,respectively.

According to this embodiment, by installing the feedwater filteringapparatuses 66 on the inlet side of the low pressure heater 57 and theinlet side and the outlet side of the high pressure heater 58,respectively, in the feedwater line 60, suspended solid contained in thefeedwater can be reduced, and it makes possible to reduce erosion insideof piping, prevention of heat transmission caused by adhering thesuspended solid to the surface of the heater tube, and a washingfrequency of the heater tube, because of the reduction effect of thesuspended solid.

Eleventh Embodiment

FIG. 15 is a basic block diagram showing a power plant of a eleventhembodiment of this invention. In addition, in this embodiment, same orcorresponding portion of the above-mentioned tenth embodiment of thepower plant is explained with assigning the same reference numeral, andonly different composition and function from the above-mentioned tenthembodiment are explained. The same is said of each embodiment of a powerplant.

As shown in FIG. 15, in the power plant of this embodiment, heater drainfiltering apparatuses 67 of any of the above-mentioned first throughninth embodiments are installed on a high pressure heater drain line 64introduced from the high pressure turbine 61 to the feedwater line 60through the high pressure heater 58 and a low pressure heater drain line65 introduced from the low pressure turbine 62 to the feedwater line 60through the low pressure heater 57, respectively.

According to this embodiment, by installing the heater drain filteringapparatuses 67 on the heater drain lines 64, 65, respectively, suspendedsolid contained in the heater drain can be reduced, and it makespossible to reduce erosion inside of piping, prevention of heattransmission caused by adhering the suspended solid to the surface ofthe heater tube, and a washing frequency of the heater tube, because ofthe reduction effect of the suspended solid.

Twelfth Embodiment

FIG. 16 is a basic block diagram showing a power plant of a twelfthembodiment of this invention. As shown in FIG. 16, similar to the tenthembodiment shown in FIG. 14, two or more feedwater filtering apparatuses68 of any of the above-mentioned first through ninth embodiments areinstalled on the feedwater line 60 between the condenser 55 and thesteam generator 59 through the condensate demineralizer equipment 56,the low pressure heater 57 and the high pressure heater 58.

That is, in the feedwater line 60, these feedwater filtering apparatuses68 are installed on the inlet side of the low pressure heater 57 and theinlet side and the outlet side of the high pressure heater 58,respectively.

Additionally, in this embodiment, a back wash line 68 connects eachfeedwater filtering apparatus 68, and the back wash line 68 is connectedto the back wash equipment 9.

According to this embodiment, in addition to acquiring the same effectas mentioned in the tenth embodiment, by installing the back washequipment 9 corresponding each feedwater filtering apparatus 68, it ispossible to always sustain original performance of each feedwaterfiltering apparatus 68.

Thirteenth Embodiment

FIG. 17 is a basic block diagram showing a power plant of a thirteenthembodiment of this invention. As shown in FIG. 17, in the power plant ofthis embodiment, similar to the eleventh embodiment shown in FIG. 15,heater drain filtering apparatuses 70 of any of the above-mentionedfirst through ninth embodiments are installed on a high pressure heaterdrain line 64 introduced from the high pressure turbine 61 to thefeedwater line 60 through the high pressure heater 58 and a low pressureheater drain line 65 introduced from the low pressure turbine 62 to thefeedwater line 60 through the low pressure heater 57, respectively.

Additionally, in this embodiment, a back wash line 71 connects eachfeedwater filtering apparatus 71, and the back wash line 71 is connectedto the back wash equipment 9.

According to this embodiment, in addition to acquiring the same effectas mentioned in the tenth embodiment, by installing the back washequipment 9 corresponding each heater drain filtering apparatus 70, itis possible to always sustain original performance of each heater drainfiltering apparatus 70.

Additionally, in the twelfth and thirteenth embodiments, besides orinstead of the back wash equipment 9, the above-mentioned chemical washequipment or the scrubbing air supply equipment 12 can be installed inthe power plant.

Fourteenth Embodiment

FIG. 18 is a basic block diagram showing a power plant, which is aexample of installing a filtering apparatus of any of theabove-mentioned first through ninth embodiment in a boiling waterreactor (BWR) power plant.

As shown in FIG. 18, the power plant of this embodiment is equipped witha feedwater line 60 on which feedwater flows from a condenser 55 to anuclear reactor pressure vessel 72 through a condensate demineralizerequipment 56, a low pressure heater 57 and a high pressure heater 58.

Moreover, the power plant of this embodiment is equipped a main steamline 63 from the nuclear reactor pressure vessel 72 to the high pressureturbine 61 and the low pressure turbine 62, and a high pressure heaterdrain line 64 introduced from the high pressure turbine 61 to thefeedwater line 60 through the high pressure heater 58 and a low pressureheater drain line 65 introduced from the low pressure turbine 62 to thefeedwater line 60 through the low pressure heater 57, respectively.

In this BWR power plant of this embodiment, two or more feedwaterfiltering apparatuses 66 of any of the above-mentioned first throughninth embodiments are installed on the feedwater line 60 between thecondenser 55 and the nuclear reactor pressure vessel 72 through thecondensate demineralizer equipment 56, the low pressure heater 57 andthe high pressure heater 58.

That is, in the feedwater line 60, these feedwater filtering apparatuses68 are installed on the inlet side of the low pressure heater 57 and theinlet side and the outlet side of the high pressure heater 58,respectively.

Moreover, in the BWR power plant of this embodiment, heater drainfiltering apparatuses 67 of any of the above-mentioned first throughninth embodiments are installed on a high pressure heater drain line 64introduced from the high pressure turbine 61 to the feedwater line 60through the high pressure heater 58 and a low pressure heater drain line65 introduced from the low pressure turbine 62 to the feedwater line 60through the low pressure heater 57, respectively.

According to this embodiment, by installing the feedwater filteringapparatuses 66 on the inlet side of the low pressure heater 57 and theinlet side and the outlet side of the high pressure heater 58,respectively, and installing the heater drain filtering apparatuses 67on the heater drain lines 64, 65, respectively, suspended solidcontained in the feedwater and the heater drain can be reduced, and itmakes possible to reduce erosion inside of piping, prevention of heattransmission caused by adhering the suspended solid to the surface ofthe heater tube, and a washing frequency of the heater tube, because ofthe reduction effect of the suspended solid.

Fifteenth Embodiment

FIG. 19 is a basic block diagram showing a power plant, which is aexample of installing a filtering apparatus of any of theabove-mentioned first through ninth embodiment in a pressurized waterreactor (PWR) power plant.

As shown in FIG. 19, the PWR power plant of this embodiment is equippedwith a feedwater line 60 on which feedwater flows from a condenser 55 toa steam generator 74 through a condensate demineralizer equipment 56, alow pressure heater 57, an air evacuator 73, and a high pressure heater58. Here, the air evacuator 73 discharges a noncondensable gas to outeratmosphere with a little steam, and a moisture separator 75 installedbetween the high pressure turbine 61 and the low pressure turbine 62 andconnected to the air evacuator 73 through a moisture separator drainline 76 removes drops which exist in the steam.

Moreover, the power plant of this embodiment is equipped a main steamline 63 from the steam generator 74 to the high pressure turbine 61 andthe low pressure turbine 62, and a high pressure heater drain line 64introduced from the high pressure turbine 61 to the feedwater line 60through the high pressure heater 58 and a low pressure heater drain line65 introduced from the low pressure turbine 62 to the feedwater line 60through the low pressure heater 57, respectively.

Furthermore, in this PWR power plant of this embodiment, two or morefeedwater filtering apparatuses 66 of any of the above-mentioned firstthrough ninth embodiments are installed on the feedwater line 60 betweenthe condenser 55 and the steam generator 74 through the condensatedemineralizer equipment 56, the low pressure heater 57, the airevacuator 71, and the high pressure heater 58.

That is, in the feedwater line 60, these feedwater filtering apparatuses68 are installed on the inlet side of the low pressure heater 57 and theinlet side and the outlet side of the high pressure heater 58,respectively.

Moreover, in the PWR power plant of this embodiment, heater drainfiltering apparatuses 67 of any of the above-mentioned first throughninth embodiments are installed on a high pressure heater drain line 64introduced from the high pressure turbine 61 to the feedwater line 60through the high pressure heater 58 and a low pressure heater drain line65 introduced from the low pressure turbine 62 to the feedwater line 60through the low pressure heater 57, respectively. And a moistureseparator drain filtering apparatus 77 of any of the above-mentionedfirst through ninth embodiments is installed on the moisture separatordrain line 75 on the moisture separator drain line 76 from the moistureseparator 75 and the air evaporator 73.

According to this embodiment, by installing the feedwater filteringapparatuses 66 on the inlet side of the low pressure heater 57 and theinlet side and the outlet side of the high pressure heater 58,respectively, installing the heater drain filtering apparatuses 67 onthe heater drain lines 64, 65, respectively, and installing the moistureseparator drain filtering apparatus 77 on the moisture separator drainline 76, suspended solid contained in the heater drain can be reduced,and it makes possible to reduce erosion inside of piping, prevention ofheat transmission caused by adhering the suspended solid to the surfaceof the heater tube, and a washing frequency of the heater tube, and achemical decontamination frequency of the steam generator 74, because ofthe reduction effect of the suspended solid.

Sixteenth Embodiment

FIG. 20 is a basic block diagram showing a power plant, which is aexample of installing a filtering apparatus of any of theabove-mentioned first through ninth embodiment in a thermal power plant.

As shown in FIG. 20, the power plant of this embodiment is equipped witha feedwater line 60 in which feedwater flows from a condenser 55 to anevaporator 77 through a condensate demineralizer equipment 56, a lowpressure heater 57, a fuel economizer 78, and a high pressure heater 58.The fuel economizer 78 collects residual oxygen to be reused.

Moreover, the power plant of this embodiment is equipped a main steamline 63 from the evaporator 77 to the high pressure turbine 61 and thelow pressure turbine 62, and a high pressure heater drain line 64introduced from the high pressure turbine 61 to the feedwater line 60through the high pressure heater 58 and a low pressure heater drain line65 introduced from the low pressure turbine 62 to the feedwater line 60through the low pressure heater 57, respectively.

In this thermal power plant of this embodiment, two or more feedwaterfiltering apparatuses 66 of any of the above-mentioned first throughninth embodiments are installed on the feedwater line 60 between thecondenser 55 and the nuclear reactor pressure vessel 72 through thecondensate demineralizer equipment 56, the low pressure heater 57 andthe high pressure heater 58.

That is, in the feedwater line 60, these feedwater filtering apparatuses68 are installed on the inlet side of the low pressure heater 57 and theinlet side and the outlet side of the high pressure heater 58,respectively.

Moreover, in the thermal power plant of this embodiment, heater drainfiltering apparatuses 67 of any of the above-mentioned first throughninth embodiments are installed on a high pressure heater drain line 64introduced from the high pressure turbine 61 to the feedwater line 60through the high pressure heater 58 and a low pressure heater drain line65 introduced from the low pressure turbine 62 to the feedwater line 60through the low pressure heater 57, respectively.

According to this embodiment, by installing the feedwater filteringapparatuses 66 on the inlet side of the low pressure heater 57 and theinlet side and the outlet side of the high pressure heater 58,respectively, and installing the heater drain filtering apparatuses 67on the heater drain lines 64, 65, respectively, suspended solidcontained in the feedwater and the heater drain can be reduced, and itmakes possible to reduce erosion inside of piping, prevention of heattransmission caused by adhering the suspended solid to the surface ofthe heater tube, because of the reduction effect of the suspended solid,and a washing period before starting the thermal power plant can beshortened.

Moreover, this invention is not limited the above-mentioned embodimentsand several change of the embodiments can be considered. For example, infrom the fourteenth to the sixteenth embodiments, it explains there arefiltering apparatuses in both feedwater line 60 and the heater drainlines 64, 65, however, it is possible that the filtering apparatusesinstalled in either one line.

Furthermore, in from the tenth embodiment to the sixteenth embodimentfor applying the filtering apparatus or device mentioned any of from thefirst embodiment to the ninth embodiment to the power plant, it mayinstall the filtering apparatus or device having the filter moduleheated in or permeated with hot fluid by using a treatment equipmentsuch as one shown in FIG. 4. And it is also possible that afterinstalling the filtering apparatus or device in the power plant thethermal treatment or thermal filtration process is carried out towardthe filter module in the filtering apparatus or module.

According to this invention, a filtering device can be made durable inhot water, and suspended solid contained in hot water can be removedcertainly. As a result, water quality of filtrate can be kept adequate.

According to this invention, by adding thermal treatment to afluororesin filter at a temperature of less than the melting point ofthe fluororesin before the use, elution from the filter can be reducedand the control water quality can be satisfied, and it can preventdamage of the filter due to heat cycle and lowering of permeabilitypreviously.

According to this invention, in the back wash operation for removingsuspended solid contained in water, such as low temperature condensate,hot feedwater, and heater drain, it makes possible to simplify the backwash operation to avoid the filter being hydrophobic without process tomake the filter hydrophilic.

Furthermore, according to this invention, suspended solid in thefeedwater or the heater drain can be reduced and it makes possible toreduce erosion inside of piping, prevention of heat transmission causedby adhering the suspended solid to the surface of the heater tube, and awashing frequency of the heater tube, because of the reduction effect ofthe suspended solid. And the suspended solid in hot water, such asfeedwater and heater drain, can be removed with keeping stablepermeability, without polluting water quality.

The foregoing discussion discloses and describes merely a number ofexemplary embodiments of the present invention. As will be understood bythose skilled in the art, the present invention may be embodied in otherspecific forms without departing from the spirit or essentialcharacteristics thereof. Accordingly, the disclosure of the presentinvention is intended to be illustrative, but not limiting, of the scopeof the invention, which is set forth in the following claims. Thus, thepresent invention may be embodied in various ways within the scope ofthe spirit of the invention.

1. A filtering device, comprising: a filtering apparatus composed of avessel with a filtrate accumulation space provided in an upper sidethereof and a filter contained in the vessel; a feed inlet line forintroducing feed into the filtering apparatus; a filtrate outlet linefor letting filtrate flow out of the filtering apparatus; the filterfiltering the feed to let filtered feed flow as the filtrate; a backwash tank for storing back wash water to be supplied into the filteringapparatus, with a partition which easily passes liquid component andhardly passes gas component to separate the back wash tank into a firstcompartment and a second compartment; the first compartment beingadapted for connecting a gas supply line capable of controlling gaspressure and for supplying the gas to the filtering apparatus, and amake-up water supply line for supplying the back wash water to thefiltering apparatus; and the second compartment being connected to thefiltrate accumulation space of the filtering apparatus.
 2. The filteringdevice as recited in claim 1, further comprising: a first leak valveinstalled in a first leak valve connected to the filtrate accumulationspace of the filtering apparatus for discharging air out of the filtrateaccumulation space; and a second leak valve installed in a second leakline connected to the first compartment of the back wash tank fordischarging air out of the first compartment of the back wash tank. 3.The filtering device as recited in claim 1, wherein: the partition ofthe back wash tank is composed of one of a hydrophilic film andhydrophilic packed material.
 4. The filtering device as recited in claim1, wherein: the partition of the back wash tank is formed in one ofhollow shape, a shape of pleats, a flat film, and a cylinder.
 5. Thefiltering device as recited in claim 1, wherein: the filter in thefiltering apparatus is made of fluororesin treated beforehand by atleast one of adding thermal treatment to the filter in at least one ofgas and liquid and penetrating the filter through at least one of hotwater and steam.
 6. A filtering device, comprising: a filteringapparatus composed of a vessel with a filtrate accumulation spaceprovided in an upper side thereof and a filter contained in the vessel;a feed inlet line for introducing feed into the filtering apparatus; afiltrate outlet line for letting filtrate flow out of the filteringapparatus; the filter filtering the feed to let filtered feed flow asthe filtrate; a drain line for discharging fluid in a lower side of thefiltering apparatus out of the filtering apparatus from an inlet side ofthe feed; and a cooler installed in the drain line for cooing thedischarging fluid.
 7. The filtering device as recited in claim 6,further comprising: a steam supply line for supplying steam into thefiltering apparatus from an outlet side of the filtrate.
 8. Thefiltering device as recited in claim 6, wherein: the filter in thefiltering apparatus is made of fluororesin treated beforehand by atleast one of adding thermal treatment to the filter in at least one ofgas and liquid and penetrating the filter through at least one of hotwater and steam.
 9. A power plant, comprising: a steam generator forgenerating steam from feedwater; a turbine driven by the steam suppliedfrom the steam generator; a condenser for condensing the steam extractedfrom the turbine into condensate; a feedwater line for supplying thecondensate from the condenser to the steam generator as the feedwater; aheater for heating the feedwater flowing in the feedwater line; a heaterdrain line for supplying drain discharged from the heater to thefeedwater line; and the filtering device according to claim 1, installedin at least one of the feedwater line and the heater drain line.
 10. Aback wash method for back washing a filtering apparatus composed of avessel and a filter made from fluororesin to which thermal treatment isadded by using at least one of gas and liquid beforehand, the vesselbeing composed of a first compartment in which the filter is containedto filter feed in a filtering operation and a second compartmentpositioned above the first compartment to contain filtered feed asfiltrate in the filtering operation, the back wash method comprising:first back washing the filter composed of, supplying back wash rinsefluid composed of at least one of water, air and steam into thefiltering apparatus from the second compartment side of the filteringapparatus, passing the back wash rinse fluid through the filter, anddischarging the back wash rinse fluid out of the filtering apparatus;and second back washing the filter composed of, supplying back washwater into the filtering apparatus from the first compartment side ofthe filtering apparatus, passing the back wash water through the filter,and discharging the back wash water out of the filtering apparatus fromthe second compartment side of the filtering apparatus.
 11. The methodas recited in claim 10, wherein: in the second back washing of thefilter, flow of the back wash water is adjusted so that a differencebetween a pressure of the first compartment and a pressure of the secondcompartment is not less than a bubble point of the filter.
 12. Themethod as recited in claim 10, further comprising: scrubbing the filterafter the first back washing of the filter before the second backwashing of the filter composed of, supplying scrubbing air into thefiltering apparatus from the first part of the filtering apparatus toshake the filter by the scribing air, and discharging the scrubbing airout of the filtering apparatus.
 13. A power plant, comprising: a steamgenerator for generating steam from feedwater; a turbine driven by thesteam supplied from the steam generator; a condenser for condensing thesteam extracted from the turbine into condensate; a feedwater line forsupplying the condensate from the condenser to the steam generator asthe feedwater; a heater for heating the feedwater flowing in thefeedwater line; a heater drain line for supplying drain discharged fromthe heater to the feedwater line; and the filtering device according toclaim 6, installed in at least one of the feedwater line and the heaterdrain line.